I filled my car up at a wal-mart gas station yesterday and they were selling SUPER unleaded at regular price because they were out of regular. So I filled my car up with that. It drove home fine, and then I drove town for about 15 minutes with no problem. And then all day today I would get a lot of hesitation, especially in low RPMs. It feels fine for awhile and then feels bumpy and hesitant again. Usually it feels a lot like I am shifting in the wrong gear when I am not. Sometimes when I start from a stop it REALLY has a hard time going.

What could my problem be?

Try replacing the fuel filter. If problem persists, and platinum spark plugs have 40,000 miles on them, I would replace them.